Tubular knitted fabric typically is manufactured on circular knitting machines in semi-continuous lengths of tubular fabric. In most cases, the tubular fabric is processed through finishing and even cutting while retained in tubular form. Typically, such processing includes a number of wet processing stages, such as washing, bleaching, sometimes dyeing, etc. At the end of this wet processing stage, the fabric is dried and prepared for finishing.
In a typical conventional wet processing line for tubular knitted fabric, the semi-continuous tubular fabric, at the end of the wet processing stage, is directed over an internal spreader device, which is designed to restore the fabric width to some desirable and appropriate dimension. In this respect, it will be understood that knitted fabric is inherently unstable geometrically (as distinguished from woven fabric, which is rather stable), and typically becomes substantially elongated in length and reduced in width, by reason of the lengthwise tensions applied to the fabric during wet processing. After passing over the spreader, the fabric conventionally goes through extractor rolls, in the form of one or more opposed sets of resilient nip rollers. These serve to physically displace water from the fabric, typically reducing the percentage of water to, say, 85% (meaning 85 pounds of water per 100 pounds of dry fabric). Typically, the fabric is then treated in a tensionless dryer, which usually is either steam heated or direct fired with gas. A typical dryer apparatus for this purpose is shown in the Frezza U.S. Pat. No. 3,496,647.
With conventional practices, in a two drum dryer of the type shown in the before mentioned U.S. Pat. No. 3,496,647, there may be a maximum drying capacity of approximately 350 pounds of water per hour. In the more economical dryer units, particularly the direct fired units, the drying costs at current energy cost levels typically are on the order of 1.5 cents per pound of water removed.
Pursuant to the present invention, significant economies are realized by utilizing in advance of the conventional dryer apparatus a so-called Mach nozzle, particularly of the type described and claimed in the Brugman U.S. Pat. No. 4,137,045. The nozzle is arranged to act on the tubular knitted fabric in advance of the dryer and serves to remove a substantial portion of the liquid content of the fabric before the fabric enters the dryer. The nozzle treatment serves to reduce the liquid content of the fabric well below the 85% level, achievable with conventional roller extraction, typically, to under 50%, thus greatly reducing the workload on the dryer for a given amount of fabric. With the nozzle treatment according to the invention, energy costs per pound of water removed are significantly less than with conventional drying arrangements. Accordingly, significant overall production cost savings are achieved. In addition, since a given amount of fabric has significantly less water to be removed by the dryer, the operating rate of the entire processing line, which tends to be limited by the dryer capacity, can be greatly increased.
The theoretical advantages of the so-called Mach nozzle system are well known from the disclosure of the Burgman U.S. Pat. No. 4,137,045, which even suggests its applicability to knitted fabrics. Nevertheless, it has been conventional wisdom that the Mach nozzle procedures could not be employed with knitted fabrics, at least tubular knitted fabrics, because of the high distortability of such fabrics and the need for maintaining the fabric under significant tension during penetration of the fabric by the high velocity steam jet. Thus, while the patent itself states that the processing of knit wear can be accomplished, the wisdom of people skilled in the art, has been that such processing could not in fact be carried out, at least on a basis that would enable a commercially acceptable product to be realized at a commercially acceptable cost basis.
In accordance with the present invention, a novel procedure and apparatus is provided, which indeed does enable tubular knitted fabric to be effectively processed and dried, using a Mach nozzle treatment stage in advance of a tensionless dryer.
Pursuant to one aspect of the invention, wet processed fabric may be taken directly from a truck or similar container and is spread to flat form and predetermined width while still in wet form. The wet, spread fabric is then discharged directly into a resilient control nip, comprising a pair of opposed resilient rollers. From this roller pair, sometimes referred to as entry-side rollers, the fabric is guided downward and around the high velocity nozzle and then upwardly to an exit-side pair of resilient rollers. According to one aspect of the invention, the respective pairs of rollers make very light contact with the fabric, so as not to crease the fabric edges, but sufficient, nevertheless, together with the degree of wrap-around of the fabric about the lower rollers, to provide relatively positive control over the movement of the fabric.
In typical mill practice, pre-drying extraction operations are usually carried out on an off-line basis from the dryer proper, because such operations can be performed at much greater rates of speed than the rate of operation of a typical dryer. Thus, the extraction equipment may service more than one dryer, and, in many cases multiple strings of tubular knitted fabric are run side by side through the dryer. Nevertheless, it is contemplated by the invention that the fabric may be processed by the Mach nozzle section on an in-line basis with the dryer, perhaps with a plurality of nozzle sections feeding two or more webs to a single dryer.
The procedures and apparatus of the invention make it possible, contrary to conventional wisdom, to process highly distortable tubular knitted fabric by means of the Mach nozzle system, and enable very significant economies in energy costs to be realized, as well as significant increases in processing speed with concomitant reduction in labor costs per production unit.
The procedures of the invention are additionally advantageous with respect to the application of wet-on-wet foam processing. In general, the use of foam-based chemicals in the processing of fabrics is advantageous because the lower liquid content of the foam-based chemicals reduces subsequent drying costs. However, the application of foam-based chemicals to wet processed fabric has not, under conventional practices, enabled consequential savings to be realized because of the high residual content of the incoming fabric. Pursuant to the present invention, however, the liquid level of the incoming fabric is sufficiently low that the low moisture content of the foam-based chemicals results in a meaningfully low total liquid content after foam processing.
For a better understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment of the invention and to the accompanying drawings.